The invention relates to an apparatus for winding of force transmitting elements made of uni-directional fiber strands constituting a fiber reinforced material. Conventionally such winding machines comprise a winding core and a supply device as well as an impregnating device for the fiber strands. The winding core and the strand supply device are arranged for relative movement between each other so that the laying down of windings or turns on the winding core is controllable by controlling the relative movement between the supply device and the winding core.
Force transmitting elements of this type which are made of uni-directional fiber strands are presently frequently used where large uni-directional loads occur, for example, for connecting the wings or blades of a helicopter rotor to the rotor head. Such force transmitting elements frequently have a loop or bight shape, whereby the fiber direction within the force transmitting element extends in the load transmitting direction. As mentioned, such load or force transmitting elements are suitable for securing the rotor blade of a helicopter rotor to the respective hardware components of the rotor head. Heretofore such force transmitting elements have either been made in a rather expensive manner by a hand winding operation or they have been wound by a machine as disclosed in U.S. Pat. No. 4,226,916 corresponding to German Patent Publication (DE-OS) No. 2,736,124.
It is necessary that such force transmitting elements have uniform physical characteristics. At the very least, a set of force transmitting elements, for example comprising four such elements to be installed in a rotor, should have the same physical characteristics for each of its elements.
It is necessary to make sure that all force transmitting elements of a set have substantially the same physical characteristics in order to minimize any variations in shape and loadability to thereby enable the construction of a balanced helicopter rotor. Such uniformity calls for a precise and time consuming manufacturing operation of the individual elements. Variations from element to element occur especially when the tension load of the fiber strand as it is being wound onto a core is subject to variation during the winding of the force transmitting element. The prior art methods, regardless whether they involve manual or machine windings, have not been satisfactory in assuring the required uniformity for at least a set of four force transmitting elements which are required in the manufacturing of a helicopter rotor.